Pressure switch



A g- 1950 R. K. SEDGWICK 2,520,660 I PRESSURE SWITCH Filed June 27, 1947 g 1.16 20 66 4 70 76 3. r -i8 INVENTOR. I EoerZ/Z Patented Aug. 29, 1950 PRESSURE SWITCH Robert K. Sedgwick, Oak Park, Ill., assignor to American Steel Foundries, Chicago, 111., a corporation'of New Jersey Application June 27, 1947, Serial No. 757,495

1 This invention relates to pressure switches and more particularly to a novel pressure responsive switch actuator adapted for use in connection with hydraulic devices, such'as hydraulic presses, to open and close electrical circuits operable in well known manner to control the operation of such devices by controlling the hydraulic circuits associated therewith. i

The hydraulic press industry has for many years needed a pressure switch which would operate at pressures up to three thousand pounds per square inch, would have a long life in service, and would operate consistently with respect to the cut-in and cut-out pressure values. Resilient materials heretofore utilized for switch actuating diaphragms have not been satisfactory inasmuch as relatively sensitive materials, such as rubber, have proved unsuitable for the lack of suliicient strength tovresist high pressures; and

relatively stiff materials, suchas steel and beryl- .2 lium copper, have proved too rigid to afiord sufli-c cient sensitivity and operating range when made sufficiently strong. Various switch actuators have been used with diaphragms having borderline strength so that. after relatively few operations the diaphragms have failed. Furthermore, many switches have been designed utilizing spring loaded plungers; however, such plungers must be lapped to substantially eliminate friction thereby involving prohibitive costs.

A general object of the invention is to provide a novel pressure responsive switch actuator which is strong enough to have a substantial safety factor and fatigue resistance yet flexible enough to have a substantial deflection under load thereby aifording sensitivity and accommodating close adjustment. i c r The above object is accomplished, according to the present invention, cby utilizing two resilient members in series, one of said members being subjected to the pressure to which the switch is responsive. is adapted to displace a fluid medium partly confined by the other resilient member which is very sensitive and thus relatively weak. The latter member is adapted to actuate an associated make and break element of the switch. The strong member may be constructed to any desired size to afford any desired volumetric displacement of the fluid. for. any given stress, and the sensitive to any desired linear displacement.

Another object of the invention is to provide novel means for adjusting a switchactuator, such This member is'relatively strong and 7 Claims. (Cl. 200-83) as above described, by acting upon the fluid medi- I um at a point remote from the resilient elements Still another object of the invention is to design a switch, such as above described, wherein the fluid medium has a coeliicient of thermal expansion approximately equal to that of the metal parts so as to reduce the effect of varying temperatures to a minimum. A further object ofthe inventionris to provide 0 in a switch, such as above described, novel means 1 for automatically compensating variations in temperature to which the device is subjected. I

The foregoing and other objects and advantages of the invention will become apparent from a consideration of the following specification and the accompanying drawings wherein:

(Figure 1 is a central vertical cross sectional view through a preferred embodiment of the-inelevation for clarity; i Figure. 2 is a fragmentary view corresponding to Figure 1 and illustrating a novel temperature. compensation device which may be utilized with the embodiment illustrated in Figure l; and

Figure 3 is a view taken on the line 3-4 :of

Figure 2., l a T Describing the invention in detail and referring first to Figure 1, the preferred embodiment of the invention illustrated therein comprises a Q. .metal body or housing 2 with an internal chamber 4 closed at one end by a cap 6 with a filler plug 8 to accommodatefilling and draining'of. the chamber 4, as hereinafter discussed. The opposite. end of the body. 2- is provided with -aseparable shank i0 securedby a nut .l2threaded thereon. The shank I0 is provided with an. axial passage l4 adapted for connection to an associ-- ated source of pressure to which the deviceis responsive.

sand pounds per square inch without overstressing the tube. The-tube It thus forms a very strong flexible partitionor wall separating the, chambers 4 and I8 and adapted to be distorted by the pressure within thechamber 18 so as to. displace variable volumetric quantities of an associated fluid within the chamber 4.

a The chamber 4 is preferably filled with afluid medium by removal of the plug 8 and thegpre vention, portions of the structure being .shown-irr ferred fiuid is one, such as glycerine, having, as nearly as practicable, the same coeflcient of thermal expansion as the metals utilized in the device. However, it will be understood that the broad aspect of the invention is afforded by any hydraulic fluid.

The body 2.isrprovidedwith a,.pprt.or opening 22 closedi by a diaphragm 24 carryinggabutton:

26 adapted'to actuate a make and break element 28 of an associated precision snap-action switch.

30 of conventional design. The switch 30 is mounted on a support plate 32 for movement therewith to and from the buttonjfi to,.adjust., the spacing between the buttonandgthemlement.

28. The plate 32 is pivoted at 34th a fulcrum bracket 36 on the body 2 and the upper end of the plate 32 is provided with a slot 38 receiving:

ment of-theplate- 32 towardthe body 2;. Thus, by'meansi of the bolt andnut assembly 40; 44,.

the distance between the button. 26 andlthe element28may-be readily adjustedto accommodate.

calibration of. the. device.

The body 2is also provided with .another.-.open-.

ing or put 50 closed by adiaphragm .52. urged inwardly toward the chamber, 4 by acompression.

spring; 54 seated againsta cap, or. closure plate secured in any convenientmanner. to..the-bodv,

2; The-diaphragm 52 is. adjustedby athreaded.

pin orstem 58" secured to abossfillcarried. by the diaphragm and actuamadjby a. nut 162i and l a lock nut 64.

initial bias into the system so.thatiwith the-tube IS in normal unstressedcondition, the switching diaphragm 24;. is, at a predetermined. distance. from the element 28; If fitlisdesired toadiust.

the device; to actuate the element 2.8. at alower.

pressure, the, nut 62v is turnedlcounterclockwise, so-that the spring 54 urges the setting diaphra m.

'2 inwardly thereby bulging the switching diaphragm 24 outwardly so. that less displacement. ofjthe fluid in..the chamber, 4.by distortion'of. the tube] Bis requiredjto actuate .the .elementzt...

To; adjust. the device so,that the element.28 is actuatedat. a. higher, pressure value. than the.

pressurefluidsubiect .to pressure variations, such.

as:.are.. common inthe hydraulicv circuit. of an hydraulic press. The tube l6 under. load. as: sumes a barrel-like shape andexpandsandcom, tracts, with increase and. decrease, respectively,

of'the pressure in .the chamber. [8. The desired.

displacement of thefluid' withinthe chamber 4 maybe regulatedbyvarying the size of J the. tube l6: Inasmuchas the sensitivity. of the deviceis dependent upon the displacement of the, fluid within the chamber and not upon the percentage. distortion ofthe tube IS, a device, suchasabove described, may be readily constructed with any 7 desired degree. of sensitivity. combined with .any desiredldegree of ruggedness. Thus,.if, one de;-. vice, constructed according to the invention,

The diaphragm... 52, is. a,. setting. diaphragm whichisv effective to introduce: an.

should fall under any given set of service conditions, a more rugged switch may be constructed on the same principle with the same degree of sensitivity.

Referring now to Figures 2 and 3 illustrating a device identical to that shown in Figure 1 except ashereinafter, discussed,,,the :parts of the device shown in Figure -21corresponding withithose of Figure 1 are identified by corresponding nul merals.

A temperature compensation device is generally-designated at 66, said device comprising a portor utlet.68,communicating with the chamber 4'andclosedlb'y a flexible, preferably corrugated, ,diaphragm..10- which is secured to a connectinglug II on one end of a :S ylphon bellows 12; theopposite end of which is provided with a connecting lug 13 secured to a bar or bridge 14, which is interlocked with the body 2 in any convenient manner, as, for example, by. lugs .16, extendingintothe passage 18: The bellows "is operable to resist'in tension outward bulging ;of-' thediaphragm 10" due to displacementof; the

. hydraulic'medium within thechamberfl; However, any changes. in thetemperature of this medium areitransmitted fto. the bellows 12"which thus expands and "contracts to, automatically adjust theppsition of the. diaphragm '10" thereby compensating forexpansion and 1 contraction oi thevariouselements ofithedevicedue to temperature. changes ,therein, It. may, be noted in this connection, thatthe -variouscomponents or the-device, includingthehydraulic. medium. are

preferably. formedi of materials having. approxie mately. the ,samecoefiicient of,thermal expansion.

Ii desired, 1 the diaphragms 24 1 and..52 may be.

corrugated inthesame mannenasthediaphragm It..is..-to. be understoodthat .I.do..not- .wish .to. e

1imited by-,-the exact embodiment; of the. device shown which is. merely-,by,way-.,of illustration and. not limitation .as. various. and other. forms. .of..the. deyicewilLbf course, be-apparentto those skilled. in .the..artvwithout.departing, from the spirit of; the.. inventi0n-;or the: scope. of ,the claims.

11' Aipressureeresponsive switch actuator come prising-gan; outer; hydraulic; chamber, an. innerchamber disposed within. thd. outer. chamber, means .for connecting oneof, said chambers to an. associated. source 7 of. pressurer to. :which. said actuator;isresponsiye a relatively, strong flexiblepartition separating saidchambers. an hydraulic medium -,in .the other chamber; adapted .to, .be displaced by; distortion. of; said. partition, aport communicating with said other chamber, arelae tively. weak. and sensitive partition. across said port adapted ito. .be:distor,ted displacement or said .medium,. aswitchmake- ,-and break; element associated with.said sensitive. partition .for actual-.- tionthereby, and. temperature compensatingmeans comprising .a diaphragm confining. anontionof. said.-medium: spaced; from said partitions;-

and, thermally. expandable and contractablee resilient. means.contacting said. medium and,connected. to.said diaphragm for yieldinglv. resist ing: movement. thereof, in response to displace-- ment of. said.medium-.

2.; Anactuator, according to .claimi, wherein meansare-provided for adiustingethe. distance between, saidelement and :said. sensitive parti,- tion, comprising means independent of said partitions-for. displacing said. medium.

cylindrical steel bulb within said chamber, means for connecting the interior of said bulb to an associated pressure to which said actuator is responsive, a port in said chamber, a diaphragm closing said port and formed of material substantially more yielding than said bulb, and a switch make and break element supported ad- J'acent said diaphragm for actuation thereby during flexure thereof due to variation in the amount of hydraulic fluid displaced by said bulb.

4. A hydraulic device for actuating a switch element comprising a body and a flexible cylindrical tube therein defining a chamber in the tube and a chamber externally thereof, said tube being capable of withstanding pressure in excess of 2000 pounds per square inch without permanent deformation and without breaking, means for connecting one of the chambers to an associated source of pressure to which the device is responsive, the other member being entirely filled with liquid and having a port, a diaphragm closing said port and formed of material more sensitive to pressure than said tube, and a switch make and break element disposed externally of said port and associated with said diaphragm for actuation thereby.

5. A pressure responsive switch actuator comprising a bulb having an internal chamber adapted for connection to an associated source of pressure to which said actuator is responsive, a body of hydraulic fluid confined against the outside of said bulb, a flexible wall confining a portion of said body, a switch make and break element associated with said wall for actuation thereby upon distortion thereof by displacement of said fluid, and temperature compensating means characterized by a diaphragm confining a portion of said body spaced from said walls, and thermally expandable and contractable resilient member contacting said fluid and connected to said diaphragm for yieldingly resisting movement thereof in response to displacement of said fluid.

6. An actuator, according to claim 5, wherein means are provided for adjusting the actuator, comprising means confining a portion of said fluid spaced from said walls, and adjustable means for moving said confining means to displace variable amounts of said fluid.

'7. An hydraulic device for actuating an associated switch element, comprising an outer chamber containing hydraulic liquid, an inner chamber within said outer chamber and defined by a cylindrical flexible steel wall having its exterior surface contacting said liquid, said inner chamber being defined by an interior surface of said wall, a passage for connecting the inner chamber to an associated source of pressure to which the device is responsive to actuate said element, and a flexible diaphragm more sensitive to pressure than said wall, said diaphragm being in contact with said liquid whereby expansion of said wall due to increase of pressure against said inner surface flexes said diaphragm.

ROBERT K. SEDGWICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,685,211 Beck 11 Sept. 25, 1928 1,822,408 King Sept. 8, 1931 1,915,498 Kellett June 27, 1933 2,080,661 Hill May 18, 1937 2,395,007 Leupold Feb. 19, 1946 

